The invention relates generally to internal combustion piston engines, fluid pumps and similar machines and, more particularly to an X-Engine assembly.
The objective of an engine designer is to provide the best function with regards to performance and efficiency, while also minimizing the amount of noise and vibration that emanate from the engine. It is also desirable to provide an engine that is the smallest, lightest-weight while having a design which can be economically manufactured and serviced.
The most widely used engine configurations in use and today are in-line, “V” and horizontally-opposed or ‘flat’. Almost all of these engines use conventional connecting rods (“con rods”) in the power conversion system whereby each piston in the engine is coupled to the crankshaft such that there is one con rod per piston in the engine. In a typical “V”-engine, each crankpin on the crankshaft is coupled to two piston-and-con rod assemblies with the two cylinder banks being offset to each other along the axis of the crankshaft to allow the two connecting rods coupled to each crankpin to be side-by-side. In this way, there is an engine main bearing on each side of every crankpin bearing, and each crankpin bearing is sufficiently sized to provide adequate bearing area for two the connecting rod “big-end” bearings so that the resultant bearing pressures encountered as the engine runs are within acceptable range. If an engine is designed having more than two con rods are attached to each crankpin there may be a compromise for either the bearing area of the crankpin or main bearings, or the cylinder bore spacing or the structure of the crankshaft and/or cylinder block that must withstand high cyclic loading. Hence, it has been found that the “V”-engine having two con rods per crankpin allows for an engine design which is satisfactory with regards to having sufficiently strong cylinder block structure, crankshaft structure between the main bearings and crankpin bearings, and acceptable bearing pressures at critical bearing interfaces such as the big-end con rod bearings.
The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion of a shaft or vice-versa, and has been demonstrated to be suitable for use in internal combustion piston engines. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating crankshaft, with a bearing block is fitted in between the crankshaft and the yoke to provide a cylindrical-cylindrical interface at the crankpin and flat-on-flat interface with the yoke so that the contact pressures at both interfaces are at acceptable levels. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed of the crankshaft.
The scotch yoke mechanism can be used in a double-ended or “double-acting” fashion such that each reciprocating assembly has a piston at either end, hence a benefit of the double-acting scotch yoke is that it can be used in an X-engine configuration having two reciprocating assemblies for a total of four pistons coupled to each crankpin bearing on the crankshaft in a similar way to the conventional con rod as it is used in “V”-configuration engines which have two con rod and piston assemblies coupled to each crankpin bearing on the crankshaft. By doubling the number of cylinders coupled to each crankpin bearing, the Double-Acting Scotch Yoke used in X-configuration can result in a significantly smaller and lower mass engine for a given bore & stroke and number of cylinders when compared with in-line, “V” and flat engine configurations.
Another advantage of the Double-Acting Scotch Yoke (“DASY”) X-Engine over conventional “V”-engines is that the fluid motion inside the crankcase is reduced because opposite pistons simply push air in between them, whereas in “V”-type engines and in-line engines there is a larger mass of fluid in motion inside the crankcase (for a given bore/stroke and number of cylinders) which is pushed out of the cylinders and around the engine's bulkheads in a way that causes larger amounts of fluid friction and necessitates having an empty volume in the engine crankcase between the crankshaft and the oil sump to allow this fluid motion to occur.
Furthermore, the DASY is a mechanism that provides true ‘harmonic motion’ or pure sinusoidal motion. Thus, DASY engine configurations which have first-order balance have perfect balance, whereas engines which have con rods always have imbalances which are unresolved due to the complex nature of the piston motion using the con rod mechanism which results in multiple orders of vibration of the 1st, 2nd and higher orders.
It should also be noted that a radial engine that employs a master con rod with secondary con rods attached to it is an arrangement which allows more than two cylinders of an engine to be coupled to a single crankpin bearing, but the compromise here is that there are at least two different piston motions (piston displacement versus crankshaft angle) occurring in this type of engine, which greatly complicates any efforts to achieve balance of even the 1st-order of vibration. Hence, there is no practical method to have 1st and 2nd order balance for a group of cylinders connected in this way. Furthermore, with the modern fuel injection systems used in engines now, having different piston motions would greatly complicate the calibration and emission-ability of such an engine. Hence, the X-engine configuration using the double-acting scotch yoke has the potential to provide a superior result for many piston engine applications, which today are mostly “V”, in-line, and flat engines that employ con rods.